Magnetic Moment Characterization for Small Satellites

Abstract

Small satellites are gaining popularity in a wide range of applications where attitude systems require high precision performance. One of the main sources of errors, in case of magnetic attitude control systems, is the residual magnetic moment (RMM) of the spacecraft. To keep the RMM low and stable, mitigation methods shall be applied based on the satellite’s magnetic dipole moment (MDM) characterization, which shall be measured accurately. For small satellites, the most common technique involves the generation of a field-free region for the magnetic measurements using a test bed. The test bed measurement setup is normally mechanical, where measurements from the device under test (DUT) are very tedious. Optical magnetic test beds (OMTB) are being developed for MDM characterization providing simpler set ups and faster measurements than mechanical test beds.

In this work, accuracy of OMTB of Aalto University has been evaluated by measuring three permanent magnets in two configurations. The measurements show a relationship between the estimation accuracy and the DUT’s marker area seen by the camera. Moreover, it was observed that the field-free region generated by Helmholtz coil cage can generate false data points. Based on these observations, the detection of the marker’s positions have been evaluated using the view area (VA) and the pointing angle (PA). The analysis shows that there is a consistent pattern depending on the combination of the VA and PA. Hence, the method of data acquisition was improved in order to prioritize the markers which position allow better accuracy. The achieved improvement of MDM estimation results is 2 %, and the test bed's overall error evaluated is a 13 % in MDM position estimation and 23 % in MDM magnitude estimation. The improved OMTB was used to characterize the MDM of four magnetic attitude coils of Foresail-1 satellite. The measurements results are consistent with design parameters, showing three dipole configuration in all coils with a MDM magnitude order of 10^-2 A·m2.